The present invention relates to an apparatus for handling constituent elements of a reactor core, and particularly to a technique of handling fuel assemblies, control rod assemblies, and control rods of the core by utilizing a common apparatus.
FIG. 6 shows a conventional example of the reactor structure of a fast breeder reactor. The structure shown in FIG. 3 which was reported in "SUPERPHENIX NEWS" issued on March, 1987 is similar to the structure of a fast breeder reactor shown in FIG. 6. As shown in FIG. 6, the fast breeder reactor has a reactor vessel 1 and a roof deck 2 which covers the upper portion of the reactor vessel 1. The roof deck 2 comprises a large rotating plug 3 and a small rotating plug 4 which can rotate independently of each other. The vessel which is covered in this manner contains a core 5, a primary coolant sodium 6 which removes the heat generated by the nuclear reaction of the core 5, a circulating pump 7 for forcibly circulating the primary coolant so as to pass it through the core 5, and an intermediate heat exchanger 8 for performing heat exchange between the primary coolant whose temperature is increased by being passed through the core and a low temperature secondary coolant which is supplied from the outside of the vessel.
The large rotating plug 3 is disposed so that it can rotate relative to the roof deck 2, and the small rotating plug 4 is disposed so that it can rotate relative to the large rotating plug 3. A core upper mechanism 9 and a fuel exchanger 10 are provided in the small rotating plug 4. In addition, as shown in FIG. 7, the core 5 comprises as core constituent elements core fuel assemblies 11, blanket fuel assemblies 12, control rod assemblies 13, moving neutron shields 14, and fixed neutron shields 15. The side of the core 5 is provided with a transit pot for receiving the core constituent elements for a while before they are taken off to the outside of the reactor, so that the core constituent elements are carried out of the furnace from the transit pot in a fuel bucket by means of a fuel handling machine (not shown). An example of such a fuel handling machine is discussed in NUCLEAR TECHNOLOGY, Vol 68 (Feb. 1985) pp. 160-170.
Of the core constituent elements, the core fuel assemblies 11, the blanket fuel assemblies 12, the control rod assemblies 13, and the moving neutron shields 14 are required to be exchanged with new elements outside of the furnace or reactor, while the fixed neutron shields 15 need not be taken out of the furnace during the lifetime of a plant and are remained disposed in the furnace, as suggested by the name. Of the fuel assemblies which are brought into and removed from the furnace, the core fuel assemblies 11, the blanket fuel assemblies 12, and the moving neutron shields 14 all have the structure shown in FIG. 8 which comprise a handling head 16 at the upper end thereof for engaging with the claws of a gripper of the fuel exchanger, thereby allowing the assembly to be handled by the fuel exchanger. As shown in FIG. 9, each of the control rod assemblies 13 comprises a guide tube 17 and a control rod 18, in which a handling head 19 of the control rod 18 is gripped by the claws of a gripper of a control rod drive mechanism when the output of the core is to be controlled, so that each control rod can be moved longitudinally. In addition, when the control rod assemblies 13 are brought into or removed from the furnace or reactor, each of the assemblies 13 can be handled by gripping the upper end of the guide tube 17 by means of the claws of the gripper of the fuel exchanger.
FIG. 10 shows a fuel exchanger. As shown in the drawing, the fuel exchanger 10 has a fuel exchanger body 20 which is supported by chains 24 operated by a winch 23 so that the body can be moved upward and downward, and a guide sleeve 21. The fuel exchanger body 20 is provided for the purpose of gripping each of the core constituent elements, and the guide sleeve 21 is provided on the body 20 for the purpose of preventing swinging of the gripper during an earthquake. The fuel exchanger body 20 is driven upward and downward through the chains 24 and comprises claws for gripping the core constituent elements, a claw-operating shaft 26 for closing and opening the claws 25, and a claw driving apparatus 27 for driving upward and downward the claw-operating shaft 26 with an external cylinder which prevents the transverse vibration of the claw-operating shaft 26. As shown in FIG. 11, the claw-operating shaft 26 is pulled by the claw-driving apparatus 27 in order to grip the core constituent elements, and the fuel exchanger body 20 is moved downward to a position right above a given core constituent element in a state wherein the lower ends of the claws 25 are closed so that the claws 25 can be inserted into the handling head 16 of that core constituent element. As shown in FIG. 12, the claw-operating shaft 26 is moved downward by the claw-driving apparatus 27 so that the lower ends of the claws 25 are opened and engaged with the handling head 16 of the core constituent element. In this state, the fuel exchanger body 20 is moved upward by an elevating drive mechanism 23 so that the core constituent element can be taken out of the core. When a new fuel is charged into the core, the above-described operation may be performed in the reverse order. An analogue of this fuel exchanger is described in Japanese Patent Laid-Open No. 137293/1981.
FIG. 13 shows a control rod drive mechanism 28 which can be roughly divided into a drive mechanism part 29 and an upper guide tube part 30. The upper guide tube part 30 is supported on the upper surface of the small rotating plug 4 and is provided in the furnace including the primary coolant sodium 6 and argon atmosphere, the lower end being connected to a control rod 18 through the gripper 31. The drive mechanism 29 is accommodated in in a core upper mechanism 32 placed above the small rotating plug 4 and adjacent to the uppermost portion of the upper guide tube part 30. The gripper 31 is closed and opened by operating an operational shaft 10 in a similar manner to that in the fuel exchanger.
Although, as described above, an apparatus for handling the core constituent elements comprises the fuel exchanger and the control rod drive mechanism, the diameter of the small rotating plug is large and the diameter of the large rotating plug is hence large too, because the fuel exchanger as well as the core upper mechanism containing the control rod drive mechanism are provided on the small rotating plug in the above-described reactor. In addition, the diameters of the small and large rotating plugs are determined to be large in value so that the fuel exchanger can gain access to all the core constituent elements to be handled upon rotation of the two rotating plugs. Therefore, there has been a limit in reductions in the diameter of the large rotating plug in the prior art when attempts have been made to reduce the size of the structure of the fast breeder reactor and to reduce the construction cost thereof.